The following correction was printed in the Guardian's Corrections and clarifications column, Tuesday July 3 2007

We were wrong to say that part of the Tour de France would be staged in Britain for the first time next weekend. It is the first time the tour has come to London, or started in Britain, but stages were held in England in 1974 and 1994.

It will be the biggest sporting event in London before the 2012 Olympics, attracting more than 2.5 million spectators for an event more synonymous with the landmarks of Paris. But next weekend, when for the first time in its 104-year history part of the Tour de France is staged in Britain, one element will remain irredeemably French. An elite team of French traffic police, the garde republicaine, will provide the motorcycle escort on the streets of London and Kent for the 189 riders taking part in the Tour.

Their British counterparts - although insisting they remain in charge - will have the more mundane task of closing off roads and manning safety barricades.

The French team, which runs a precision display similar to the Royal Signals White Helmets, has escorted the Tour since 1953. It will keep a moving protective bubble around the riders as they speed towards Canterbury on the first stage of the 22-day event. The 45 French officers will assist 4,500 Met officers and 1,800 from Kent.

With a global television audience of more than 2 billion viewers in 180 countries, the event is expected to bring an immediate tourism windfall of £115m to the south-east - and act as an unprecedented global advertising campaign for the attractions of London. More than 500,000 people are expected in central London for Saturday's prologue - a 4.9-mile sprint around landmarks including Buckingham Palace and Westminster Abbey. The next day up to 2 million spectators could line the 126-mile route to Canterbury. The event, which has taken four years to plan, is being used as an early dress rehearsal for the Olympics because of the expected huge crowds, the strain on the transport network and the record number of road closures required.

Mick Hickford, Transport for London's head of special projects, said: "It is estimated there could be 2 million people over the two days - that is probably the largest audience for a sporting event in the capital ever. If there is a dreadful deluge there could be less, if the weather is good, even more."

Promotion

The idea of enticing the Tour to London emerged during talks at City Hall with the mayor's advisers on how encouraging cyclists. "We had done a lot of work on cycle lanes and infrastructure, but we wanted a bigger promotional boost - getting a pop star on a bike would have been fantastic, but I thought we could do better and bring the biggest cycling event in the world to London."

TfL says there has been an 83% increase in cycling in the capital since 2000, with 480,000 journeys a day, but its target is a 400% increase.

Ken Livingstone, the mayor, said: "We want to use the excitement of the Tour to fuel this appetite for cycling."

For non-cycling fans there is the attraction of the publicity caravan, a cavalcade of promotional floats which precedes stages, showering spectators with freebies including cheese, mineral water, croissants and wine gums.

Gary MacGowan, TfL's technical manager, said the logistical planning had been immense: "It is like building a sports stadium in the centre of London in a couple of days." There will be 12 miles of barriers, four temporary pedestrian bridges, 18 giant TV screens - and 11,000 extra parking spaces for cyclists. About 4,800 people travel with the tour, including a huge media contingent, and 1,600 vehicles require accreditation.

Some 135 trucks are required to build the finish area in the Mall - work will start on Thursday constructing grandstands, commentary boxes and finishing gantries. At dawn on Sunday it will be taken down and reassembled in Canterbury ready for the first-stage finish.

Assistant Commissioner Tarique Ghaffur, in charge of Scotland Yard's central operations, said: "Every event is a showcase for the Olympics and we are keen to use these as test events."

The Met is promising officers will adopt a "light touch". Inspector Stuart Cornish, of the public order planning unit, said: "The passion of the European cycle fans means the organisers like crowds to get as close as possible - when they pat the riders on the back it does not mean they want to knock them off."

Tour in numbers

45 Squad of French officers from the Garde Républicaine who will join 6,300 British officers to police the Tour

4.9 Length in miles of the race prologue, from Whitehall to The Mall.

£115m Amount expected to be reaped in a tourism windfall from staging the Tour in the south-east.

83% Increase in cycling in London since 2000; the target is a 400% increase.